The present invention relates to a control device for an internal combustion engine having at least one cylinder including at least one intake valve and at least one exhaust valve having fully variable valve-gear assembly which is individually controllable for each cylinder, and a method of controlling the operation of an internal combustion engine having at least one intake valve and at least one exhaust valve having fully variable valve-gear assembly which is individually controllable for each cylinder.
Conventional internal combustion engines have one or more camshafts for controlling the engine valves, with a predefined valve lifting curve. The valve lifting curve is fixedly defined by the design of the camshaft. A fixed valve lifting curve for the intake and exhaust valves of the internal combustion engine does not permit optimal operation of the internal combustion engine in every operating condition, however, since different internal combustion engine operating conditions generally require different valve lifting curves.
Because of the fixed valve lifting curve, control of charge cycles in the cylinders is only possible to a limited degree, and cannot be optimized for all operating conditions. The term charge cycle refers to expelling exhaust gas from the combustion chamber and filling the combustion chamber of a cylinder of the internal combustion engine with fresh air, possibly added fuel, andxe2x80x94depending on the operating condition and the nature of the internal combustion enginexe2x80x94recirculated residual gas from a previous combustion cycle.
Various fully variable valve drive mechanisms for the intake and exhaust valves have been proposed for variably controlling the charge cycle in the cylinders of an internal combustion engine. With fully variable valve operation, the engine valve processes are flexible. This means that quantities of fresh air and residual gas introduced into the cylinder are controlled by varying the instant of opening and/or closing and/or the opening and/or closing speed and/or the lift of the intake and exhaust valves. Known fully variable valve drive mechanisms are for example electromagnetic solenoid valve control SOLV and electro-hydraulic valve control. Also known are mechanical fully variable valve drive mechanisms such as variable valve timing control VVT in combination with lift control.
Using electromagnetic and electro-hydraulic valve control, the operation of the internal combustion engine does not require provision of a camshaft. Thus the adjustment dynamics, i.e., the extent of possible changes in the instants of opening and closing of the intake and exhaust valves, of the opening lift and the opening and closing speed, are limited only by the mechanical design of the intake and exhaust valves and of the corresponding valve actuators. This means that for every work cycle of a current cylinder the gas charge of the current cylinder may be adjusted independently of a gas charge of a cylinder which is ahead of it in the ignition sequence, and may be adjusted independently of a gas charge of the current cylinder in a previous work cycle.
A control system for an internal combustion engine having fully variable valve operation usually has an engine control unit and a valve control unit which are connected to a software bus system such as a CAN bus. In the engine control unit, control signals are determined for a throttle valve, a fuel injector, a spark plug, and for the valve control unit based for example on output signals from a crankshaft angle sensor, a lambda probe, a hot film air mass sensor, and an intake pipe pressure sensor. The control signals for the valve control unit are conveyed via the software bus system to the valve control unit. The valve control unit translates the control signals into instants of opening and closing for the intake and exhaust valves, an opening lift of the intake and exhaust valves, and an opening or closing speed of the intake and exhaust valves. These control systems transmit a very high volume of data via the software bus system under an operating condition having load cycle processes at high rotational speeds. Accordingly, it is necessary to dimension the software bus system appropriately, i.e., to over-dimension it for normal operating conditions.
FIG. 6 shows a model which illustrates a calculation of a desired charging of a cylinder with fresh air to achieve a setpoint torque, as used for example in the Bosch ME7 engine controller. Using a setpoint torque misetpoint and a rotational speed nmot of the internal combustion engine as input values, with provision for a setpoint lambda efficiency etalamsetpoint and a desired spark angle efficiency etazwsetpoint, a desired fresh air charge rldesire of the cylinder for realizing an induced setpoint torque is calculated. The desired charge rldesire is calibrated to 100% with the displacement volume of the cylinder filled with fresh air at 1.013 mb at 0xc2x0 C. The input value misetpoint is the setpoint value of the induced torque, which is calibrated to 100% at a charge of 100% fresh air, a lambda xcex=1.0, and optimal spark angle. The input value nmot specifies a rotational speed of the internal combustion engine.
The calculation model illustrated in FIG. 6 for calculating the desired charge of the cylinder with fresh air to achieve a predefined setpoint torque is used today with combustion engines having a throttle valve. This calculation model is inadequate for combustion engines having fully variable valve operation.
The object of the present invention is to provide a control device for an internal combustion engine having fully variable valve-gear assembly, characterized by simple construction, and a simple method of controlling operation of an internal combustion engine having fully variable valve-gear assembly.
This object is achieved according to the present invention using a control device having the features recited in claim 1 and a method having the features recited in claim 10.
Advantageous variants of the present invention derive from the subclaims.